All methods of lifting gas, oil, or water from subterranean wells, referred to as “artificial lift”, are utilized when the well is deficient of sufficient internal pressure to push the fluid to the ground surface. Of the long-established various methods of lift, the jet pump, or venturi, or eductor, has been sparingly utilized since the early twentieth century. They all work on the concept of conservation of energy, and subsequently, Bernoulli's Principle, stating that the total pressure head in an ideal non-compressible flowing fluid remains the same at any given point in the flow stream. So, by constricting the flow, as in a converging nozzle, the stream must flow faster. And, when flowing faster, Bernoulli's Principle illustrates that the associated stream pressure must decrease. This decrease is often utilized, as in a jet pump to draw in other objective fluids to be transported with the original stream.
A conventional jet pump generally includes a jet pump housing, a nozzle having a converging nozzle bore in the jet pump housing, a nozzle tip which communicates with the nozzle bore and terminates in a nozzle chamber, a mixing chamber which communicates with the nozzle chamber and a diverging passage called diffuser which communicates with the mixing chamber. As it flows through the nozzle, a pressurized power fluid creates a smaller, higher velocity stream which draws a suction fluid (the objective fluid) into the nozzle chamber and further into the mixing chamber. The mixed fluid velocity reduces in the diverging, diffuser passage following the mixing chamber, increasing the pressure of the fluid. The fluid mixture is transported to a selected station. Jet pumps are suitable for a variety of applications including downhole well applications in which the pumps may be used to retrieve well reservoir fluid containing hydrocarbons to the well surface.
In typical downhole hydrocarbon production applications, the jet pump housing of a jet pump is directly or indirectly attached to a tubing string which is inserted in a well bore, above but in a line connected with the packer, a common device long utilized by those skilled in the art. Power fluid is pumped from the ground surface through the tubing string into the jet pump. As the power fluid flows through the nozzle in the jet pump housing, reservoir fluid from the well bore is drawn from below the packer, through the standing valve 102 (or safety valve, known by those skilled in the art) into the jet pump via a pressure drop generated by the power fluid exiting the nozzle. This reservoir fluid mixes with the power fluid. The fluid mixture, which includes power fluid and reservoir fluid, flows through the jet pump to the well annulus area between the pump housing and well casing to the well surface or up the tubing string in case of reverse flow.
One of the limitations of conventional jet pumps which are used in hydrocarbon well production applications is that the diffuser and/or other components of the jet pump may be immovably attached to the jet pump housing. Consequently, these components hinder downhole cleaning and/or maintenance operations in the well bore below the pump and thus, the tubing string must be removed from the well bore for jet pump housing removal in order to perform these operations. One exception to this is the use of a smaller size conventional jet pump mounted inside a sleeve. This sleeve matches the O.D. and I.D. of the tubing string. This smaller jet pump is removable/retrievable in its entirety by wireline, thereby leaving maintenance to the well below the pump.
In subterranean wells, the jet pump flow stream, or power fluid, is pumped from the ground surface and may include water, oil or gas. The generated Venturi pressure drop is used to draw in reservoir fluid, and the surface pump pressure pushes the combined power fluid and reservoir fluid to the surface where the two are separated, and the operation of artificial lift is continuous.
Standards within the well drilling and production industries have evolved over time, and these standards apply to safety and convenience. The standards include specifications for well casing and tubing and the relationships these have to each other in size. So, for any given well, there are established ranges of dimensions for the production tubing or tubing string and the casing. These fixed dimensions set the limits for tooling sizes such as those for jet pumps. By design, jet pumps operate at very high fluid flow velocities. These flow velocities, in combination with differing well conditions. frequently produce undesirable and often unpredictable undesirable effects on the mechanical components of jet pumps. Downhole reservoir condition variables can include varying fluids constituencies, fluid constituency percentages variation, entrapped gasses, high temperatures, high and varying pressures, corrosives, and solid contaminants, some of which can be very abrasive.
In consideration of all of these well variables, along with the need to minimize the cost of operating the jet pump and lifting the combined fluids to the surface, the jet pump design becomes a very important factor in the operation. Jet pumps often require 3000 to 4500 psi power fluid surface pump pressure to operate, combined with another 3000 to 4500 psi to lift the fluid to the surface. Production capacities for jet pump wells can vary widely but frequently reach 4000 barrels per day. and can reach more. The result is a surface pump system which is large and quite costly. In addition to this. the cost of electrical power to operate the surface pump system can be substantial, particularly in times of economically depressed commodity prices.
Therefore, it becomes imperative for the jet pump to operate as efficiently as possible, reliably, and uninterrupted for as long as possible. Maintaining operational efficiency of a well requires constant attention to the well variables. As the variables change, there can be differing production equipment demands. Performance of jet pumps is directly related to the component sizes and resulting output stream magnitude. Also, conditions of the well often impart abrasive wear or erosion on jet pump components. These conditions necessitate maintenance, and accordingly, retrieval of the jet pump to the surface. All of this work must be performed as efficiently as possible.
Because subterranean formations are dynamic, wells require maintenance. As discussed above, there can be a variety of effects to the casing and production tubing from natural reservoir activity. Results may include plugging of the well, perforations, safety valve or standing valve (check valve), or simply buildup of paraffin or scale on the tubing surfaces, along with a host of other maintenance-requiring occurrences. These conditions require clear access through the tubing and jet pump to the lower well depths.
Some wells exhibit casing which may be old and deteriorated or may be vulnerable to abrasive/corrosive contaminant entrained reservoir fluid flow. Conventional jet pump-configured wells operate by surface power fluid pumped down the production tubing, and this along with production fluids lifted in the annulus between the tubing and the casing. Where this is not allowed due to casing erosion concerns, the reverse procedure must be utilized. Therefore, optimum design of a jet pump should include features in addition to good metallurgical practices for long erosion, corrosion, and abrasive wear life as follows:
1. Simple design with no moving, and minimal number of components;
2. Through-flow hydraulically optimized, with fewest fluid turns, most gradual turns, most gradual divergences, minimal laminar flow interruptions and largest flow port cross-sectional areas possible;
3. Capability of efficient reversing of the jet pump assembly (nozzle and mixing tube) for lifting production fluid up either the annulus or the tubing;
4. Capability of reliable, efficient, ordinary, and possible frequent removal of the jet pump assembly, while in the well, leaving the unobstructed bore of the jet pump housing, which dimensionally closely matches the internal diameter of the connecting production tubing;
5. Performance which minimizes surface pump power requirements; and
6. Results in maximum possible production.
Accordingly, this invention describes a high flow capacity reversible operation jet pump which includes a housing that is attached to a tubing string and from which a jet pump assembly including the functional components of the jet pump can be selectively removed from the housing while the housing remains in place in the tubing string, allowing for unobstructed cleaning and/or maintenance of the well bore. A high flow capacity reversible operation jet pump which includes a jet pump assembly that can be selectively re-oriented in the jet pump housing to facilitate reversible operation, in combination with the fore-stated through accessibility, of the jet pump is included. The jet pump is streamline improved for more efficient flow. Flow through the jet pump exhibits reduced velocities via larger flow ports, as suction ports are located inside the housing walls away from the jet pump assembly.